Knapweed

Knapweed is in the genus, Centaurea, a group of "herbaceous thistles and thistle-like flowering plants in the family Asteraceae".
Wikipedia

This flower is in its early stage of opening. It becomes much fuller as it matures.

In an Ontario wildflowers website, the author identifies this flower as Spotted Knapweed - Centaurea maculosa.
Wildflowers of Ontario

There are several species (and subspecies, apparently) of Spotted Knapweed and classifying them (as with many other plants) can be very confusing, especially when common names are used. To complicate matters, the same name is sometimes used for different plants, depending on geographical or cultural location.

The scientific classification is far more precise (though there are discrepancies of opinion even in the scientific realm). Here is an example of the standard set of hierarchical categories that all plants have a place in:

Kingdom Plantae -- Plants
Subkingdom Tracheobionta -- Vascular plants
Superdivision Spermatophyta -- Seed plants
Division Magnoliophyta -- Flowering plants
Class Magnoliopsida -- Dicotyledons
Subclass Asteridae
Order Asterales
Family Asteraceae -- Aster family
Genus Centaurea L. -- knapweed P
Species Centaurea stoebe L. -- spotted knapweed P
Subspecies Centaurea stoebe L. ssp. micranthos (Gugler) Hayek -- spotted knapweed P
USDA Natural Resources Conservation Service